This invention relates to means for surface mounting electrical components to a printed circuit board and will have special application to mounting electrical components by an automatic production line.
One of the most advanced changes taking place in electronics is miniaturization, the most important result of which is to place more functions in a given space. The previously employed methods of mounting chips and other components on a printed circuit board, that is, by extending leads from the components through holes in the boards and then soldering them to the reverse side, are no longer practical in most applications.
Very recently, the concept of surface mounting has been introduced. This concept has many advantages over the previous methods. The size of the boards can be greatly reduced, storage space is appreciably reduced, fewer assembly machines are required and other factors result in a major reduction in overall costs.
However, surface mounting retains one major disadvantage in that leads still must be soldered in order to connect the component to the board. Additionally, there are difficulties in positioning the chip contacts over very closely spaced board contacts and in soldering the very small connections without bridging and board warping, which can either prevent all contacts from properly connecting or can break the delicate contacts later.
As mentioned above, and more specifically, mounting techniques for connecting electrical components to the surface of a printed circuit board;s conductive pads have utilized either a wave soldering or a fluorocarbon vapor and solder paste method. Each of these methods require an extremely high temperature, typically around 500 degrees fahrenheit, to effect the attachment of a component's leads to the conductive pad. The problem involved in the use of these methods is that the high temperature creates a hostile environment for the electronic components which results in a high component breakage rate. Another problem associated with the above methods is the high cost involved in an attempt to minimize the shock effects of the high temperature. The components are slowly brought up in temperature to within 50 degrees of the soldering medium and after being soldered are slowly lowered in temperature to the ambient temperature. The heating and cooling of the components reduces the rejection rate but increased the cost of the product due to the added cost of heating and cooling the units.
These methods, however, have a distinct advantage in that the soldering of the electrical component leads results in a connection which, because of the solder, is clean, sure and corrosion resistant.
Instead of using heat to effect the connection, this invention uses a pressure sensitive adhesive and an electrically conductive medium to mechanically and electrically attach the component in place, thereby removing the expense and component rejection associated with methods utilizing a high heat source.